The Stratigraphy Machine 
               Andrew D. Miall, University of Toronto  
               John H. Holbrook, Texas Christian University 
               Summary 
               The stratigraphic record is constructed by 
               multiple geological processes acting over 
               time scales as short as a few seconds to 
               as long as hundreds of millions of years. 
               The probability of preservation of the 
               products of high-frequency processes is 
               very low. The full range of depositional and 
               removal processes constitutes what may 
               be termed a “Stratigraphy Machine.” 
               Sedimentation rates and time 
               scales 
               Peter Sadler (1981) generated a graph 
               that has long puzzled geologists –  he      Figure 1. Sadler’s (1981) relationship explained 
               demonstrated that sedimentation rates  in terms of the range of geological processes 
               vary inversely with the duration of the  that generate the sedimentary record. The 
               elapsed time over which these rates are     numbers in the boxes refer to a proposed 
               measured, from the temporary flood-plain    “Sedimentation Rate Scale” (Miall, 2015). 
               deposits beside a river to the complete fill 
               of a major sedimentary basin. This relationship has been referred to as the “Sadler effect.” 
               Lengthy sections representing long time periods include a large number of sedimentary breaks. 
               In fact, Ager (1973) remarked that the sedimentary record is “more gap than record.” However, it 
               has taken the maturation of sedimentology and stratigraphy to provide a complete explanation of 
               the Sadler effect. 
               The science of stratigraphy has been revolutionized over the last fifty years. The emergence of 
               sequence stratigraphy as the standard method for documentation and analysis, the increased 
               sophistication of facies analysis and other sedimentological methods of documentation and 
               interpretation, and the increasing accuracy and precision of the Geological Time Scale, have 
               enabled ever more refined interpretations of geological processes. It can now be demonstrated 
               that the sedimentary record is a product of the simultaneous action of a range of geological 
               processes acting over a range of rates and time scales, ranging from seconds to hundreds of 
               millions of years (Miall, 2015; Figure 1). 
               The stratigraphy machine 
               The stratigraphic record does not represent a simple accumulation of sediment over millions of 
               years, but is a complex amalgam of the products of short, intermediate, and long-term processes, 
               interrupted by hiatuses and unconformities generated over a  similar  range of time scales. 
               Unconformities and other sedimentary breaks may be informally grouped into four broad classes, 
               reflecting their duration and processes of causation (Miall, 2016). In most sedimentary sections, 
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        as little as 10% of the elapsed time represented by the section is recorded by actual sediment 
        (e.g., see Miall, 2014; Bhattacharya et al. 2019). These processes may be formalized in the 
        concept of a “Stratigraphy Machine”, as illustrated in Figure 2.  
        This figure represents an attempt to express in tabular form the hierarchy of processes that 
        generate and remove sediments over the full range of geological time scales. For convenience, 
        the time scale is subdivided into four broad and overlapping time ranges. To read the diagram, 
        enter at the red arrow on the left. Sediments are generated by depositional processes, with 
        preservation (downward directed red arrow) or removal (upward directed black arrow) creating 
        the initial succession. With the passage of time, longer-term processes affect the succession 
        (diagonal yellow arrow), with preservation and/or removal acting over the progressively longer 
        time scales. High-frequency processes are episodic or gradual over extended time periods and 
        affected by longer term processes. Thus, as implied by the nested loops at the base of the 
        diagram, a longer allocyclic process or 
        episode will affect the autogenic processes 
        operating at the shorter time scales. 
        Sufficient time (≥107 years) must elapse for 
        all geological processes to complete at least 
        one full cycle. Numerous sedimentary 
        breaks of various durations are generated at 
        all stages, as indicated by the wavy 
        unconformity symbol crossed by the upward-
        directed black arrows. The end product is the 
        preserved rock record, and is represented by 
        the lowermost box at the right. This shows 
        the preservation of a basin fill by the long-
        term accommodation driven by plate-
        tectonic processes, for example, the slow 
        thermal subsidence at an extensional 
        continental margin. A guide to the use of this 
        diagram and its application to stratigraphic 
        interpretation is in press (Holbrook and Miall, 
        in press). 
        References                Figure 2. The Stratigraphy Machine 
        Ager, D. V., 1973, The nature of the stratigraphical record: New York, John Wiley, 114 p. 
        Bhattacharya, J., Miall, A. D., Ferron, C., Gabriel, J., Randazzo, N., Kynaston, D., Jicha, B. R., and Singer, S., 2019, 
          Balancing sediment budgets in deep time and the nature of the stratigraphic record: Earth Science Reviews. v. 199, 
          102985, 25 p.  
        Holbrook, J. M., and Miall, A. D., in press, Time in the Rock: A field guide to interpreting past events and processes 
          from a cryptic and fragmentary clastic archive: Earth Science Reviews. 
        Miall, A. D., 2014, The emptiness of the stratigraphic record: A preliminary evaluation of missing time in the Mesaverde 
          Group, Book Cliffs, Utah: Journal of Sedimentary Research, v. 84, p. 457-469. 
        Miall, A. D., 2015, Updating uniformitarianism: stratigraphy as just a set of “frozen accidents”, in Smith, D. G., Bailey, 
          R., J., Burgess, P., and Fraser, A., eds., Strata and time: Geological Society, London, Special Publication 404, p. 
          11-36.
        Miall, A. D., 2016, The valuation of unconformities: Earth Science Reviews, v. 163, p. 22-71. 
        Sadler, P. M., 1981, Sedimentation rates and the completeness of stratigraphic sections: Journal of Geology, v. 89, p. 
          569-584.
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